Field of the Invention
The present invention relates to a method for manufacturing a gas sensor including a ceramic sensor element.
Description of the Background Art
Conventionally, there have been well known gas sensors having sensor elements formed from an oxygen-ion conductive solid electrolyte ceramic, such as zirconia (ZrO2), as devices for determining the concentrations of predetermined gas components in measurement gas, such as combustion gasses and exhaust gasses in internal combustion engines such as automobile engines.
Such gas sensors generally include a sensor element (detection element) with an elongated plate shape which is made of a ceramic, wherein the sensor element is secured by a plurality of ceramic supporters which are ceramic insulators and by powder compacts made of ceramics such as talc which are embedded between the ceramic supporters, in a hollow portion of a metal housing and a cylindrical inner tube secured thereto through welding, so that the powder compacts provide hermetic sealing between a space on one end side of the sensor element and a space on the other end side of the sensor element. The hermetic sealing is achieved by pressing the ceramic supporters and the powder compacts which are sequentially and annularly mounted to the sensor element using a predetermined sealing jig to compress the powder compacts, and subsequently swaging the inner tube from outside using a predetermined swaging jig (refer to Japanese Patent Application Laid-Open No. 2015-169606, for example).
In order to secure airtightness with the hermetic sealing described above, a pressing by a sealing jig needs to be performed with a relatively high load of 400 kgf or more, for example. In addition, the sensor element needs to be disposed in a correct position in a correct attitude after the hermetic sealing so that the gas sensor satisfies desired characteristics.
If the sensor element is inclined and comes in contact with the ceramic supporters at the time of the sealing, thereby being subjected to an action of a stress from the ceramic supporters, a crack may occur in a portion of the sensor element being in contact with the ceramic supporters in a process of manufacture or in use, or the sensor element may be broken at the contact portion. In a manufacturing process, it is required that a generation of such a defective product is reduced and, if the defective product is generated, it needs to be reliably found and excluded from a shipping object.